Figure 2. Photomicrograph of cathepsin-B expression in DU4475 (A) and BT20 (B) tumors. (Original magnification, x40.) Inserts show controls without primary antibody. Cathepsin-B expression is revealed as a blue precipitate of the alkaline phosphatase-labeled secondary antibody. Note the strong cathepsin-B expression in the highly invasive DU4475 tumor (A) compared with the well differentiated adenocarcinoma (B).